Ion mobility spectrometers are commonly used to detect the presence of target compounds. Typically, in an ion mobility spectrometer a target compound is ionized, passed through an electric field and then detected by an electrode detector.
The target compound can be directly ionized by an ionization source that emits energy that interacts with and ionizes the target compound. Alternatively or additionally, the target compound can be indirectly ionized by an ionization source which emits energy that interacts with and ionizes an intermediate compound which, in turn, interacts with and ionizes the target compound.
The amount of time it takes for the ionized target compound to pass through the electric field and reach the electrode detector can depend on a number of parameters, including the mass of the ionized target compound, the charge of the ionized target compound, and the strength of the electric field. By manipulating these parameters, the ionized target compound can be detected by measuring the ion current at the electrode detector at a predetermined time.
One type of ion mobility spectrometer is based on proton transfer. In this type of spectrometer, an ionized intermediate compound transfers a proton to the target compound to form the ionized target compound, which is then passed through an electric field and detected. Generally, the proton affinity of the intermediate compound is less than the proton affinity of the target compound.
Another type of ion mobility spectrometer is based on electron transfer. In this type of spectrometer, an ionized intermediate compound transfers an electron to the target compound to form the ionized target compound, which is then passed through an electric field and detected. Usually, the ionization potential of the intermediate compound is greater than the ionization potential of the target compound.